It will be appreciated that the highly accurate sensing of temperature in a molding process system may not only lead to relevant information as to the operation of the system, or a mold therein, but may also provide information indicative of the characteristics of the melt material (e.g., density) stages to form a part. The following related patents are examples of the use of information relative to temperature of a molding system, and are also hereby incorporated by reference for their teachings: U.S. Pat. No. 6,649,095 to Buja, issued Nov. 18, 2003; and U.S. Pat. No. 4,904,172 to Buja issued Feb. 27, 1990.
As previously indicated by Buja in U.S. Pat. No. 6,649,095, it is possible to sense the mold cavity melt volume conditions in injection molding systems so that molded articles of uniform consistency and quality are produced at all times irrespective of fluctuations in the flow properties of mold resin. Disclosed was an invention that relied upon novel methods and techniques for sensing and monitoring a temperature profile at one or more locations in a molding system.
More recently it has further been determined that volumetric temperature and pressure changes can be sensed using improved micro-bead thermocouple junctions and that such devices can be used at many mold locations to accurately and reliably monitor volumetric temperature and pressure in the operation of a molding system. In one embodiment, such sensors can be placed in a machined mold part line vent groove to provide temperature and pressure data; to indicate open mold state and closed mold machine, and further monitor the melt flow volume from the initial start of melt flow in the mold process through each sequential process stage, for example, even as the melt material cures to a solid molded part.
In injection-molding machines the cyclic thermal-mechanical operating precision and stability of the equipment has been greatly improved through improvements in the control circuitry used, along with the use of “real-time” closed-loop machine process control. However, the plastic material or “melt” used to mold a part, in the injection molding industry, is produced by a complicated polymerization reaction. The occurrence of some variance in the “melt” and “flow” properties of the plastic material cannot be avoided due to variability in the raw material and difficulties in controlling the polymerization reaction. In particular, in resin materials produced by a batch method, maintaining the material properties constant from one batch to another is extremely difficult.
For example, the value of the melt-flow index (MFI—determined using a five minute static state and five minute “melt” extruding time test) often fluctuates by approximately 10% with respect to the specified value for a particular material. Furthermore, in the case of a colored material, there is a further variance in properties from one color to another due to differences in the pigments and the compounding of additives. Even if the control precision of an injection-molding machine is improved, however, a disparity of temperature-pressure melt volume density, and quality, in the molded articles arises as a result of fluctuations in resin “melt-flow,” which affects the “shrink” properties for the molded part(s). It is often the case that a fluctuation in the quality (dimension, weight, density, warping etc.) of the molded articles results when resin “melt-flow” lots are changed over from one to another. Accordingly, a technician must often monitor the molding machine and mold temperature at all times to address any fluctuation in resin “melt-flow” properties. And the technician must try to adjust the parameters for the automated melt and mold process to eliminate any variance in quality of the molded articles.
It will be appreciated that the molding process is a cyclic sequence starting from a mold open, reasonably static thermal state, to a mold close thermal-mechanical melt flow injection state of material melted and stored from the previous cycle. The present invention employs an improved thermocouple sensor, or micro-bead thermocouple with an exposed junction, to sense temperature-pressure volumetric changes as the trapped site and melt flow front gases are exhausted during the material volumetric initial fill and final pack cures in the mold cavity during the molding operation or cycle including the above-identified stages. For example, the sensor may be employed to indicate a start of the molding process sequence, where the mold open to close and clamp stage must occur before the melt flow injection occurs.
Aspects of the present invention also rely on the fact that the injection of a melt (liquid material) into a closed mold cavity forces the gases enclosed in the cavity out the mold cavity vent(s) or groove(s) put in the mold for that purpose. If the mold venting is not included, the compressed trapped gas will heat up and initiate a burn mark on the compressing melt. If a trapped gas, melt burning problem is not resolved, the burning may further erode a pit into the mold cavity.
An object of the present invention is, therefore, to provide improved methods and means for sensing temperature-pressure melt flow changes within a molding system. Accordingly, the attached figures illustrate various embodiments employed or designed to sense temperature-pressure changes in a highly-reliable and accurate manner at, for example, a nozzle, ejector pin and/or mold vent. Moreover, the system contemplates the manner in which the thermocouples are assembled relative to the mold and other system components so as to provide a system suitable for reliable and repeatable use.
As will be illustrated in the following detailed description, data obtained from one or more of the micro-bead sensors may be employed as an input to a melt/molding system controller so as to monitor the molding process consistency and optimize the performance of one or more aspects of such a system. Such a system can then be employed to analyze and optimize the injection molding process cycle, temperature-pressure density for minimum weight, and to eliminate wasteful time and energy from such cycles, while also assuring that the molding system is producing accurate parts by remaining within acceptable operational parameter ranges.
Disclosed in embodiments herein is an injection molding system, including: a multi-variable sensor comprising dissimilar metals formed into a micro-bead junction; and a programmable device, with associated memory, connected to and receiving a signal from said sensor, said programmable device periodically receiving the signal and recording said signal to record changes in said signal, wherein said programmable device is capable of storing said signals as data.
Further disclosed in embodiments herein is a sensing system for use with a molding system, including: a melt orifice, positioned such that melt material flows adjacent said orifice under normal injection molding parameters; an unsheathed sensor suitable for insertion into said orifice, said sensor further comprising a junction of dissimilar metals forming an EMF junction in direct contact with a molding material; and means for retaining the sensor in the orifice.
The various embodiments described herein are not intended to limit the invention to those embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.